Center drill



Feb. 4, 1947.

' o. ARNDT cmmsn DRILL.

'Filedflov. 6. 1944 FIG.2Q 0

INVENTOR.

OSCAR ARNDT WVMA.

ATTORNEYS Patented Feb. 4, 1947 STATES PTE 3 Claims.

The invention relates to tools for forming recess Centers in work 110 provide b@arings thereon for engagement with the supporting centers cf a lathe o1 other machine tool. Such tools ara usually formed with a small diameter drill portion and an adjacent conical reamer portion. The drill forms a clearance in the work for the portion of the supporting center adjacent its apex, while the conical reamer portion forms the bearing for engaging said supporting center. The purpose of this clearance is to form in the work a more acurate conical bearing but in actual practice lt does not always accomplish this result. This is for the reason that there are always minute inaccuracies in the cutting cf the bearing which initially throw the work into slightly eccentrlc position. Also, the rotation 015 the bearing about the non-rotating supportlng center Will ca.use wear which slightly shifts the axis of rotation. The portion cf the conical bearing nearest the axis is subjected to the greatest wear and. therefore, any inltial inaccuracy in this portion will have the greatest efiect in the subsequent shifting of the ax1s.

It; is the object of the invention to avoid the defects in centerlng tools as heretofore constructed and to this end the lnvention consists in the construction as hereinafter set forth.

In the dr'awing:

Fig. 1 is an elevation of my improved center drilling too1 drawn to an enlarged scale; and

Flg. 2 is a longitudinal sec'tion through a portion of a work member in which a recess center bearing is formed and showing the same in engagement with a supporting centen In general constructlon my improved tool is similar to tools heretofore made in having a drill portion A, an adjacent conical reamer portion B and a recess C extending longitudinally of both portions to form a cutting edge D. However. instead of forming the reamer portlon with its entire surface in a, cone having a Single apex, my improved reamer has two conlcal portions wlth different apexes. Thus, the pqrtion B which is nearest the axls has its apex slightly in advance of the portion B which is farther from the axis.

In other words, the portion B may be regardecl as a clearance, ground in the portion B. The depth of the clearance (which is exaggerated in the drawing) is very slight as, for instance, .0015 of an inch.

In the operation 0f forming a recess center in a work piece, such as E, the portion B of the tool will fashion the bearing portion E, while the portion B will cut a clearance E Consequently, when a supp0rting center F is engaged with the recess, it will first bear against the conical porti0n E thereof. As this portion is farthest from the axis and of greatest' area, inaccuracies therein will be mim'mized and, when the work is rotated upon the center F, any inaccuracy therein will be quickly eliminated. Furthermore as the rotation continues and slight wear occurs the bearing will be extended to include the area of the portion E. Thus a true bearing will be formecl which will always hold the work concentric with the same axis.

What I clalm as my invention is:

1. A center forming, tool comprising a drill and a conlcal reamer, the latter having a portion adjacent the drill, the apex of which is slightl v in advance of the apex of the remaining portion both portions beim; at the same angle to the axis.

2. A center forming tool comprising an integral drill and conical reamer, the latte1" having a porti'on of its area farthest from the apex slightly relievecl to form a parallel cone.

3. A center forming tool comprising an integral drill and conical reamer, the latter having a portion of its area farthest from the apex relieved to a depth of not more than .002 of an'inch to form a parallel cone.

\ OSCAR ARNDT.

REFERENCES CITED The following references are of record in ehe flle of thls patent:

UNI'I'ED STATES PATENTS 

